1. Field of the invention
The present invention relates to a strip line feeding apparatus for feeding a high frequency signal to a strip line.
2. Description of the prior art
FIG. 33 is a plan view of an example of the strip line feeding apparatus in the prior art, which was disclosed in Japanese Patent Application JP-A-8-250912. In the figure, reference numerals 1, 2, 3, 4, 10, 40 denote, respectively, a strip conductor pattern, an arc like conductor pattern, a through-hole for inner conductor, a tip portion of the strip conductor pattern 1, and a through-hole for a fixing bolt.
FIG. 34 and FIG. 35 are cross sectional views of FIG. 33, along the lines axe2x80x94axe2x80x2 and bxe2x80x94bxe2x80x2, respectively. In these figures, reference numerals 5a, 5b denote first and second dielectric substrates, and the reference numerals 6a, 6b denote first and second ground conductor patterns, respectively. Reference numeral 20 denotes a coaxial connector.
The strip conductor pattern 1 is formed on one side of the first dielectric substrate 5a, and the first ground conductor pattern 6a is formed on the other side of the first dielectric substrate. The second ground conductor pattern 6b is formed on one side of the second dielectric substrate 5b. The first and the second dielectric substrates 5a, 5b are disposed one over another to form a strip line. The cross sections of the strip line are shown in FIGS. 34, 35. The first and second ground conductor patterns 6a, 6b are disposed at the outer sides of the strip line, respectively.
Reference numerals 20, 7, 8, 9 denote, respectively, a coaxial connector, a central conductor of the coaxial connector, a dielectric portion of the coaxial connector, and an outer conductor of the coaxial connector.
The through-hole for inner conductor 3 is disposed at the tip portion of the strip line pattern 10, and the arc like conductor patterns 2 are formed on the first and second dielectric substrates at the side opposite to the side where the first and second ground conductor patterns are formed, so that the arc like conductor pattern 2 surrounds the through-hole for inner conductor 3.
A plurality of the through-holes for outer conductor 4 are disposed along the inner border of the arc like conductor pattern 2. The through-holes for outer conductor 4 penetrate the arc like conductor pattern 2 and connect the first and second ground patterns 6a, 6b, which are disposed at the upper and lower surfaces of the dielectric substrates. The plurality of the through-holes for outer conductor 4 form a cage having a substantially cylindrical form. The through-hole for inner conductor 3 and the through-holes for outer conductor 4 form a coaxial line structure, the characteristic impedance of which is substantially equal to that of the coaxial connector 20 and that of the strip line.
The central conductor 7 of the coaxial connector 20 is inserted into the through-hole for inner conductor 3 from the side of the first ground conductor pattern 6a of the dielectric substrate 5a. And the central conductor 7 is soldered to be fixed to the through-hole 3 so as to electrically contact thereto.
The outer conductor 9 of the coaxial connector 20 electrically contacts to the first ground conductor pattern 6a of the dielectric substrate. By the way, the central conductor 7 is supported by the dielectric portion 8 of the coaxial connector so as to be held in the inner space of the outer conductor 9 of the coaxial connector.
The through-hole 40 for a fixing bolt has dimensions identical to that of the threaded holes disposed in the flange of the coaxial connector 20 so that the flange of the coaxial connector 20 can be fixed to the first and second dielectric substrates 5a, 5b, by means of fixing bolts, which can penetrate the holes.
A high frequency signal is supplied from the coaxial connector 20 to the strip conductor pattern 1, through the through-hole for inner conductor 3. The provided signal propagates along the strip line.
The ground signal flows from the outer conductor 9 of the coaxial connector 20 into the first ground conductor 6a on the upper surface of the dielectric substrate 5a. A part of the ground signal flows in the first ground conductor 6a, which is disposed along the strip line conductor pattern 1. And the rest flows into the second ground conductor 6b through the through-hole for outer conductor 4, and flows in the second ground conductor 6b, which is disposed along the strip line pattern 1.
The coaxial line structure formed by the through-hole for inner conductor 3 and the through-holes for outer conductor 4 has dimensions substantially identical to that of the coaxial connector so that high frequency signals propagated in the coaxial line can be fed effectively to the strip line.
The strip line feeding apparatus in the prior art has drawbacks that the electromagnetic field is disturbed and the electromagnetic wave reflection characteristic is deteriorated. That is because there are discontinuous structures at the junction portion between the central conductor of the coaxial connector 20 and the through-hole for inner conductor 3, as well as at the junction portion between the through-hole 3 and the strip conductor pattern 1.
Furthermore, the junction portion between the coaxial connector 20 and the through-hole for inner conductor 3 is arranged in the inside of layered substrates, as a result, the fixing process such as soldering at the junction is difficult in the prior art. Especially when the structure in the prior art is applied in multi-layered substrates, it is necessary to dispose hidden blind through-holes. This entails to a complicated fabrication process.
An object of the present invention is to eliminate the above-mentioned drawbacks.
Another object is to propose a strip line feeding apparatus, which has a good reflection characteristic in the high frequency region.
Another object is to propose a strip line feeding apparatus, which can be easily fabricated.
The objects are attained by the strip line feeding apparatus described in the independent claims.
In an embodiment of the present invention, the strip line feeding apparatus comprises:
a first dielectric substrate, on one surface of which a strip conductor pattern is disposed, and on the other surface of which a first ground conductor pattern is disposed;
a second dielectric substrate, on one surface of which a second ground conductor pattern is disposed, the first and the second substrates are disposed one over the other so as to form a strip line so that the first and second ground conductor patterns are disposed at the outsides of the strip line;
a through-hole for inner conductor, which is connected with the tip portion of the strip conductor pattern and is penetrating the first dielectric substrate;
through-holes for outer conductor, which are disposed around the through-hole for inner conductor and are connecting the first and second ground conductor patterns disposed on the upper and under surfaces of the strip line;
and a signal feeder comprised of a signal conductor and a ground conductor, the signal conductor is electrically connected with the strip conductor pattern through the through-hole for inner conductor, and the ground conductor is electrically connected with the first and second ground pattern through the through-holes for outer conductor;
wherein a serial high impedance portion is disposed near to the connecting portion between the strip conductor pattern and the through-hole for inner conductor.
In an embodiment of the present invention, the high impedance portion is a portion disposed near to the tip portion of the strip conductor pattern, where the width of the strip conductor pattern is narrowed.
In an embodiment of the present invention, the high impedance portion is a hole disposed in the area of the second ground conductor of the second dielectric substrate just under the through-hole for inner conductor.
In an embodiment of the present invention, the strip line feeding apparatus comprises:
a first dielectric substrate, on one surface of which a strip conductor pattern is disposed, and on the other surface of which a first ground conductor pattern is disposed;
a second dielectric substrate, on one surface of which a second ground conductor pattern is disposed, the first and the second substrates are disposed one over another so as to form a strip line so that the first and second ground conductor patterns are disposed at the outside of the strip line;
a through-hole for inner conductor, which is connected with the tip portion of the strip conductor pattern and is penetrating the first dielectric substrate;
through-holes for outer conductor, which are disposed around the through-hole for inner conductor and are connecting the first and second ground conductor pattern disposed on the upper and under surfaces of the strip line;
and a signal feeder comprised of a signal conductor and a ground conductor, the signal conductor is electrically connected with the strip conductor pattern through the through-hole for inner conductor, and the ground conductor is electrically connected with the first and second ground pattern through the through-holes for outer conductor;
wherein a matching through-hole, connected with the strip conductor pattern at a point distant from the through-hole for inner conductor by about a quarter of the using wave length, is disposed in the second dielectric substrate, and penetrates the second dielectric substrate,
and short circuiting through-holes, which penetrate the first and second dielectric substrates and electrically connect with the first and second ground conductors, are disposed around the matching through-hole.
In an embodiment of the present invention, a land pattern, electrically connected with the matching through-hole, is disposed on the under surface of the second dielectric substrate in the area of the second ground conductor under the matching through-hole, the land pattern is disconnected from the second ground conductor.
In an embodiment of the present invention, the through-hole for inner conductor elongates to penetrate the second dielectric substrate.
In an embodiment of the present invention, a land pattern electrically connected with the through-hole for inner conductor, is disposed in the area of the second ground conductor on the under surface of the second dielectric substrate, the land pattern is disconnected from the second ground conductor.
In an embodiment of the present invention, the through-holes for outer conductor are disposed around the through-hole for inner conductor so as to form a cylindrical cage.
In an embodiment of the present invention, the signal feeder is a coaxial connector, the central conductor of which is inserted into the through-hole for inner conductor from the strip conductor pattern side and is electrically connected with the through-hole for inner conductor, and the outer conductor of the coaxial connector is electrically connected to the first ground conductor pattern through the through-holes for outer conductor.
In an embodiment of the present invention, the signal feeder is a micro strip line, which comprises: a third dielectric substrate disposed on the first dielectric substrate at the opposite side of the second dielectric substrate; a second strip conductor pattern disposed on a surface of the third dielectric substrate at the opposite side of the first ground conductor pattern, the tip portion of the strip conductor pattern and the tip portion of the second strip conductor pattern are arranged so that one is over the other. The through-hole for inner conductor elongates to penetrate the third dielectric substrate so that tip portion of the second strip conductor pattern is electrically connected with that of the strip conductor pattern.
In an embodiment of the present invention, further comprises:
a fourth dielectric substrate, which is disposed under the second dielectric substrate;
and a third ground conductor pattern is disposed on a surface of the fourth dielectric substrate at the opposite side of the second dielectric substrate.
The third ground conductor pattern is electrically connected with the first and second ground patterns.